FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied. The E-UMTS system is a system that has evolved from the existing UMTS system, and its standardization work is currently being performed by the 3GPP standards organization. The E-UMTS system can also be referred to as a LTE (Long-Term Evolution) system.
The E-UMTS network can roughly be divided into an E-UTRAN and a Core Network (CN). The E-UTRAN generally comprises a terminal (i.e., User Equipment (UE)), a base station (i.e., eNode B), a Serving Gateway (S-GW) that is located at an end of the E-UMTS network and connects with one or more external networks, and a Mobility Management Entity (MME) that performs mobility management functions for a mobile terminal. One eNode B may have one or more cells.
FIG. 2 shows an exemplary architecture of a radio interface protocol between a terminal and an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) according to the 3GPP radio access network standard. The radio interface protocol is horizontally comprised of a physical layer, a data link layer, and a network layer, and vertically comprised of a user plane for transmitting user data and a control plane for transferring control signaling. The protocol layer may be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based upon the lower three layers of the Open System Interconnection (OSI) standards model that is widely known in the field of communication systems.
Hereinafter, particular layers of the radio protocol control plane of FIG. 2 and of the radio protocol user plane of FIG. 3 will be described below.
The physical layer (Layer 1) uses a physical channel to provide an information transfer service to a higher layer. The physical layer is connected with a medium access control (MAC) layer located thereabove via a transport channel, and data is transferred between the physical layer and the MAC layer via the transport channel. Also, between respectively different physical layers, namely, between the respective physical layers of the transmitting side (transmitter) and the receiving side (receiver), data is transferred via a physical channel.
The Medium Access Control (MAC) layer of Layer 2 provides services to a radio link control (RLC) layer (which is a higher layer) via a logical channel. The RLC layer of Layer 2 supports the transmission of data with reliability. It should be noted that if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself may not need to exist. The PDCP layer of Layer 2 performs a header compression function that reduces unnecessary control information such that data being transmitted by employing Internet Protocol (IP) packets, such as IPv4 or IPv6, can be efficiently sent over a radio interface that has a relatively small bandwidth.
The Radio Resource Control (RRC) layer located at the lowermost portion of Layer 3 is only defined in the control plane, and handles the control of logical channels, transport channels, and physical channels with respect to the configuration, reconfiguration and release of radio bearers (RB). Here, the RB refers to a service that is provided by Layer 2 for data transfer between the mobile terminal and the UTRAN. The RBs refer to a logical path provided by the first and second layers of the radio protocol for data transmission between the terminal and the UTRAN. In general, configuration (or setup) of the RB refers to the process of stipulating the characteristics of a radio protocol layer and a channel required for providing a particular service, and setting the respective detailed parameters and operational methods. An RRC state refers to whether there exists a logical connection to exchange RRC messages between the RRC layer of a specific terminal and the RRC layer of the UTRAN. If there is a connection, the terminal is said to be in RRC connected state. If there is no connection, the terminal is said to be in idle state.
The logical channel is a channel defined between an RLC entity and a MAC entity, and may be divided according to the characteristics of data on the logical channel. The transport channel is a channel defined between the physical layer and the MAC entity, and may be divided according to a transmission scheme in which data on the transport channel is transmitted.
In general, the Common Control Channel (CCCH) is a common control channel, and is used when a terminal sends a message to a base station in a state that the terminal does not have an RRC connection with the base station, or when a terminal sends an RRC message in a state that the terminal has an RRC connection with a certain base station but if a base station to which the terminal is currently accessing is different from the base station having the RRC connection with the terminal. The CCCH is also used when the base station is to send an RRC message to a terminal having no RRC connection with the base station.
On the contrary, in RRC connected state, when the terminal and the base station exchanges control messages (e.g., RRC messages) or user data, a Dedicated Control Channel (DCCH) or Dedicated Traffic Channel (DTCH) is used. In this case, there is a need to effectively distinguish a message transmitted via the CCCH from a message or data transmitted via the DTCH/DCCH. For this, according to the related art, the base station and the terminal use a plurality of Cell Radio Network Temporary Identifiers (C-RNTI) to distinguish the above channels from each other. For instance, when notifying a transmission of the Physical Downlink Shared Channel (PDSCH) or Physical Uplink Shared Channel (PUSCH) via the Physical Downlink Control Channel (PDCCH), a C-RNTI A is used if data of the CCCH via the PDSCH or PUSCH is transmitted, and a C-RNTI B is used if data of the DTCH or DCCH is transmitted. However, this method may cause the waste of power consumption and an increase of complexity, considering that the receiving side should always monitor the plurality of C-RNTIs.
For a terminal having no RRC connection, the C-RNTI is not allocated. In this case, it is difficult to discriminate through the C-RNTI whether data belongs to which logical channel, thereby making it difficult to use the above method.
In addition, for a terminal before having the RRC connection, the terminal does not have any RB established with the base station. On the contrary, a terminal having the RRC connection has several RBs established with the base station. This signifies, from a perspective of the MAC entity serving to handle the mapping of the transport channel and the logical channel, to distinguish contents of each message transmitted/received during the RACH procedure. That is, there is a need to have a method for distinguishing each case based on the perspective of the MAC Protocol Data Unit (PDU).